The present invention relates to a process of precious metal catalyst recovery from an organosilicon product-containing liquid reaction medium containing precious metal catalyst. In particular, the present invention relates to a process of precious metal catalyst recovery from an organosilicon product-containing liquid reaction medium containing precious metal catalyst wherein the liquid reaction medium is produced by precious metal-catalyzed hydrosilation processes.
Hydrosilation reactions for syntheses of organosilicon, i.e., organosiloxane or organosilane, products are well known and generally involve catalyzed hydrosilation of an aliphatically unsaturated compound with a silane or a silicon polymer containing reactive silanic-hydrogen and/or hydrogen-siloxy units in the presence of a precious metal catalyst, e.g., platinum (Pt), rhodium and palladium. As a result, precious metal catalysts remain in organosilicon product-containing reaction media, e.g., siloxane or silane streams, causing significant precious metal waste, high color in organosilicon products, and black particle formation due to slow precious metal precipitation causing customer complaints of organosilicon products such as cosmetic and personal use products.
Organosilane distillations produce silane heavy wastes in which precious metal catalysts such as platinum catalyst remain, causing significant precious metal waste therein as well.
In certain organosilicon products, there is a low color specification. For example, a hydrosilylation product of triethoxysilane with 1-octene can have a color of less than 30 pt-co. However, the existence of precious metal catalysts such as platinum in the product causes product color, i.e., having a color of about 30-60 pt-co. As a result, heavy distillation is needed to remove precious metals and to reduce product color. This additional heavy distillation step not only reduces product yield but also significantly increases final product cost.
Current methods do not provide for desirable precious metal catalyst recovery from an organosilicon product-containing liquid reaction medium containing precious metal catalyst, e.g., a liquid reaction medium from continuous siloxane copolymer unit or a continuous silane hydrosilation unit, before the liquid reaction medium is passed to product storage containers. Further, current methods do not provide for desirable precious metal catalyst recovery from an organosilicon product-containing liquid reaction medium containing precious metal catalyst, e.g., a liquid reaction medium from a continuous silane distillation unit, before the liquid reaction medium is passed to silane heavy waste storage containers.